Urban din is forcing animal mating calls to be either unsexy or unheard.

Some people are confounded by actor Benedict Cumberbatch’s heartthrob status and compare his looks to an otter, bread dough, or…By Jenny J. Chen

Some people are confounded by actor Benedict Cumberbatch’s heartthrob status and compare his looks to an otter, bread dough, or an alien from Close Encounters of the Third Kind. But then you hear his voice. It resonates rich and deep, “like a jaguar in a cello,” wrote journalist Caitlin Moran. There is even a Facebook page devoted to his mellifluous timbre where fans join together “because we love his voice.” And if the sex appeal of his register wasn’t clear enough already, consider the popular meme that depicts a reclining Cumberbatch with the words, “Yes, my voice gets women pregnant. You’re welcome.”

From the perspective of physical anthropology, the commotion over Cumberbatch’s voice is not surprising. Studies show that women tend to be attracted to men with deep voices because it signals a large physical frame and social dominance. A sonorous voice may also indicate good reproductive health. A 2007 study of modern hunter-gatherers in Tanzania (who don’t have access to modern birth control) found that men with low-pitched voices had more children born to them. And if we think of the human voice as a mating call, Cumberbatch’s lushly low voice is the paragon.

But imagine how much of his appeal would be lost if he raised the pitch of his voice by 300 hertz.

At this higher register, Cumberbatch sounds more like Elijah Wood of The Hobbit, whose voice has been compared to a flute. Fortunately, Cumberbatch doesn’t need to artificially raise the pitch of his voice. But the Cumberbatches of the animal kingdom aren’t as lucky. A number of studies over the past decade indicate that the males of some species have been forced to forgo their sexy deep voices—sometimes by as much as 300 hertz, because they can’t be heard above the ever-growing din of our factories, freeways, and machines.

Like us, many species of animals also find lower male mating calls the most attractive.

Pitch is measured in hertz, which is the number of times per second that a soundwave oscillates. One hertz is 1 oscillation per second, and 1 kilohertz (kHz) is 1,000 oscillations per second. Take city traffic. It falls between 1 kHz and 10 kHz (with the lowest noise falling at the lower end of the spectrum). Coincidentally, that’s the exact range of pitch for some of the deepest and most attractive mating calls in many species of animals, including bow-winged grasshoppers, the southern brown tree frog, the American robin, and the Carolina wren. Studies have found that these species and many others are raising the pitch of their mating calls to adapt to urban noise. For example, certain species of frogs increased the pitch of their mating calls by 5 percent and grasshoppers increased the pitch of their calls by about 4 percent.

Hey Disney, enough with the warm and fuzzy personification of nature! Dress her in a suit and toss her a calculator because deals are going down in the jungle. Sure, some are symbioses, with two creatures partnering for mutual benefit....READ MORE

Like us, many species of animals also find lower male mating calls the most attractive. Female red deer, for example, prefer male red deer with deep roars, and the usually quiet and shy male koala bear performs a mating call like a deep belch. The blacktail shiner fish attracts his mate with a deep growl. While not widely studied, there is evidence that lower frequency mating calls advertise a male’s physical and sexual fitness. Studies link low-pitched mating calls of male birds, primates, frogs, and other animals to larger body size, higher testosterone levels, and sexual maturity.

This has led some researchers to consider whether human-generated noise is getting in the way of animals’ love lives. When animals are forced to raise the pitch of their mating calls, important information may be be lost and females have less knowledge at their disposal to pick the fittest mate.

“Females could be making poor choices,” says Kirsten Parris, a researcher at the University of Melbourne who studies the effects of urban noise on amphibians. “They can no longer hear that Bob has more energy than Frank.” Pairing up with a less energetic mate could reduce her breeding success, she says.

A few studies are bearing this out. In 2010, researchers monitored the egg-laying of the great tit bird along a busy Dutch street, and found that females laid on average 10 percent fewer eggs when the ambient traffic noise was in the 2 kHz band. This also happens to be the same frequency as the low part of the bird’s mating song. Even after researchers accounted for other factors, such as distance to traffic, tree density and type, and weather, the pitch of the traffic noise was the best predictor of clutch size. A possible reason that there are fewer eggs in the noisy areas is because the noise interferes with the females’ ability to hear the males’ song and identify good quality mates, say the scientists.

In 2006, researchers tracked pairing success and age distribution of male ovenbirds in the forests of Alberta, Canada, near noise-generating compressor stations compared with relatively noiseless places. They found significantly more inexperienced birds breeding for the first time near the noise generating compressor stations (48 percent compared with 30 percent near noiseless habitats). They also found that pairing success was much lower near compressor sites than the noise-free habitats, leading the authors to hypothesize that noise makes it hard for the females to hear the male song at a distance or “females may perceive males to be of lower quality because of distortion of song characteristics.”

But not all researchers are persuaded that noise affects animal mating calls, or if it does, whether the change in pitch is effective in coping with noisy conditions.

Sue Anne Zollinger, a research scientist at the Max Planck Institute for Ornithology says that it has become widely accepted as a general phenomenon that “animals increase pitch to avoid noise, but the truth is much less clear.” In a metastudy of bird mating calls and noise, she found that of the 56 species examined, less than half were found to have a difference in pitch in noisy areas.

Hans Slabbekoorn, an associate professor at Leiden University, who has spent 15 years studying the effects of human noise on animal song, agrees that there is “clear and replicated experimental evidence for noise-dependent shifts in the pitch of several animal species, but this does not mean that all species will change the pitch of their song.”

Slabbekoorn further stresses that “the higher pitch may make it more likely for a male’s call to be heard, but it’s not clear whether the callers of those species that do shift actually benefit, as they may lose signal quality.” Additional longitudinal studies may help to answer remaining questions about costs of masking noise and potential relief by a change in pitch. Parris is also looking into the possibility that noise has raised the pitch of the growling grass frog, and whether this has caused a loss of information and contributed to its endangerment.

While the scientists continue their research, we might take a cue from their studies so far. If you’re searching for a mate and want to be your best, sexiest self, you might want to refrain from having to yell or raise the pitch of your voice. When dating, steer clear of noisy bars or bass-thumping nightclubs and opt instead for a relatively quiet stroll in the park.

Jenny J. Chen is a science writer based in Washington, D.C. Her work has previously appeared in The Atlantic, Washington Post, NPR, and others.

The lead photocollage was created using a Benedict Cumberbatch photo from (((Fat Les)))/Flickr. All other photos were from Wikipedia.

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